My wife just informed me that her clock is currently 4+ hours slow and while driving, she can see the battery-charge warning light glowing dimly.

The battery is probably 4 years old or less, so this is my first choice. I have not had a chance to get a volt meter on it yet, but I will in a few hours.

The alternator should be fine, but you never know...

Anyone wish to place odds on the battery?

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William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

I would imagine it is the battery but look at the belt too to make sure it is tight.
engatwork

I've got $5 on the alternator.
-Larry

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03/83 300D 184k
07/73 280 160k
-88 other 153k

I believe the battery light encompasses the whole charging system. I got it recently in my 300SD. It turned out that the alternator was only producing 13v when it should be producing 14.5v. Replaced it and all was normal. Bought one from Autozone for $90 for the 55amp. It came with a lifetime warranty. Can't beat that. If you find the belt is properly tensioned and you know your battery is good, that leaves the alternator and it's built in regulator. I personally find that replacing the whole alternator is easier and saves more time.

Nolan

Check the voltage regulator.
It screws into (2 screws) the back of the alternator and the contacts may be worn down so that they are no longer making the battery charging circuit when the battery needs charging. My original Bosch alternator in my 78 300D lasted over 260K and went through at least 4 voltage regulators. Its a $40 Bosch part. I use to
keep an extra one in the car.
Hope this is of help.

Check the belt first, then the voltage regulator.

Well, here's the verdict..... battery!
The belts are fine, the alternator is charging at 13.4V on idle, the battery is just not holding the charge. Last night I drove her around for an hour and tested the battery... 12V. This morning I tested again... 9.4V.

Buying a battery today.... should be a lot cheaper with Larry's $5.00.. Ha, Ha...

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William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

Are you sure there isn't some auxillary thing on that may be draining it while it sits idle? No sense in just replacing the battery if the new one is just gonna drain as well.

just my $5.00, er....$0.02

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FrankieZ
84 500SEL EURO 87K
85 300D 267K (and still goin' strong)

Put in new battery last night and drove around for a while. Did not get the light to glow... YEA!

Checked voltage after setting for 16 hrs. and battery holding 12V+. Alternator charging at constant 13.8V and steady as a rock.

New battery fixed problem.... old one probably had bad cell.

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William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

That'll teach me!

William, how about I buy you lunch next time you find yourself in my neck of the woods? It would be worth at least 5 bucks!

-Larry (knowing he should've known better)

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03/83 300D 184k
07/73 280 160k
-88 other 153k

Larry,
Thanks for the offer... I'll take you up on it next time I'm in FL.

William